The present invention relates to a positive radiation-sensitive mixture containing a compound which forms an acid under the action of actinic radiation, and an acid-cleavable compound.
Positive radiation-sensitive mixtures in which an acid is formed through the action of actinic radiation on a photoinitiator and the acid then, in a secondary reaction, renders the irradiated regions of an acid-cleavable material soluble in an appropriate developer have been known for some time.
Of the acid-cleavable components employed hitherto in this area, the following have proven successful:
(a) those containing at least one orthocarboxylic ester and/or carboxamide acetal group, it being possible for the compounds to have a polymeric character and it being possible for the groups mentioned to occur as linking elements in the main chain or as lateral substituents,
(b) oligomeric or polymeric compounds containing recurring acetal and/or ketal groups in the main chain,
(c) compounds containing at least one enol ether or N-acyliminocarbonate group,
(d) compounds containing silyl ether groups,
(e) compounds containing silylenol ether groups, and
(f) cyclic acetals or ketals of .beta.-keto esters or amides.
As components of radiation-sensitive mixtures, acid-cleavable compounds of type (a) are described in detail in EP-A-No. 0,022,571 and DE-A-No. 2,610,842; mixtures which contain compounds of type (b) are described in DE-C-No. 2,306,248 and DE-C-No. 2,718,254; compounds of type (c) are mentioned in EP-A-Nos. 0,006,626 and 0,006,627; compounds belonging to type (d) are presented in DE-A-No. 3,544,165 and DE-A-No. 3,601,264; compounds of type (e) can be found in U.S. application Ser. No. (corresponding to DE-A No. 3,730,783), filed simultaneously; compounds of type (f) are mentioned in EP-A-No. 0,202,196.
In DE-A-No. 2,610,842, compounds containing ortho -ester or -amide acetal groups in a radiation-sensitive copying material are described which are used in the production both of printing plates and microelectronic circuits. The alcohol components mentioned for such groups are alkyl, alkenyl and aryl radicals. Good results are reported for C.sub.1 to C.sub.18 -aliphatic alcohols. Compounds based on the monoalkyl ethers of polyethylene glycols are also said to have comparable properties, the number of ethylene oxide units being, in particular, between 1 and 8. Investigations have now shown that good processing tolerances are always achieved when the alcohol component employed has a boiling point which is sufficiently high to prevent evaporation of the irradiated coating. When polyethylene glycol monoalkyl ethers are used, as when aliphatic alcohols are used, it is necessary to use relatively high-molecular-weight alcohol components. These in turn cause difficulties either with respect to the compatibility with the phenolic resins usually employed in coatings of this type or because of their effectiveness as plasticizers for the resin matrix. Finally, the etching resistance of coatings is reduced by long-chain aliphatic alcohols. Such coatings therefore survive certain process steps during production, for example of microelectronic components, with loss of resolution only.
The radiation-sensitive copying materials described in DE-A-No. 2,718,254 are also used for lithographic printing plates and for positive resists. They contain, as acid-cleavable component, an oligomeric compound containing recurring acetal or ketal units, whose alcohol component must be at least dihydric. In addition to the large range, due to the production process, within which the molecular weight or degrees of polymerization of such polyacetals may vary, the danger of introduction of contaminants into the radiation-sensitive mixture is particularly critical in the case of these acid-cleavable compounds since distillative purification is no longer possible. In addition, depending on the application conditions, the higher degree of polymerization means an increased danger of separation of the polymers employed in the case of the polymeric acetals and ketals mentioned here. This results in resolution losses, in particular when used in the submicron region.
In addition, it has recently been proposed, in contrast to the prior art, to use cyclic acetals or ketals of .beta.-keto esters or amides as an acid-cleavable component which should also be suitable for use in photoresists (EP-A-No. 0,202,196). A disadvantage of these photoresists are their low radiation sensitivity.